Field of the Invention and Related Art Statement
The present invention generally relates to a technique for detecting automatically characters, numerals and marks engraved in a side wall portion of a tire to derive tire information such as kind, size and shape of tire.
Heretofore, in order to classify or identify various tires, and operator visually reads characters, numerals and marks provided on side wall portions of tires in the form of protrusion or recesses. Hereinafter, these characters, numerals and marks are called tire information marks. Moreover, various methods for detecting automatically the tire information marks have been proposed. In one method, a side wall portion of tire is illuminated and is optically picked-up by a camera head including imaging lens and image sensor, while the tire and camera head are rotated relative to each other a constant speed.
In case of optically detecting the tire information marks engraved on the side wall portion of tire, it is very difficult to extract only the desired tire information marks, because there are formed on the side wall portion of tire various characters and marks other than the tire information marks and these undesired characters and marks might cause noise. It should be noted that a position of the tire information marks on a tire viewed in a radial direction differs for various kinds of tires and a height of the side wall portion is also varied in accordance with the width of a tire. Moreover, since the tire information marks have the same color as that of the background, an image of the side wall portion projected upon the image sensor has a very low contrast. Therefore, a photoelectrically converted signal has a very small signal-to-noise ratio.
Due to the above explained severe conditions, in the known method, the detection of the tire information marks requires a very long time period, longer than ten seconds. This results in a serious drawback of the known detecting method. That is to say, the known method could not be applied to the tire manufacturing line on which tires are fed at a period of two or three seconds. In such a case there must be provided a plurality of tire information mark detecting sections arranged in parallel with each other. This apparently results in undesired increase in cost and space.